The present invention relates to an image display system and, more particularly, to an image display system capable of easily performing an enlargement and reduction of scale of an image formed on the image surface of a graphic display apparatus.
The graphic display apparatus has a variety of uses as means for realizing various techniques using computers such as CAD (Computer-Aided-Design), CAM (Computer-Aided Manufacture) and the like. For instance, the graphic display apparatus is effectively utilized in instantaneously drawing the locus of movement of a tool or the shape of the work, in the operation of NC (Numerical Control) machine tool to permit the check of NC processing program.
In the use of the graphic display apparatus for displaying an image, it is an indispensable function to be able draw the picture of any desired portion of the image at any desired magnification. To this end, it is necessary to appoint the region of the image to be displayed at an enlarged or reduced scale, as well as the magnification.
Hitherto, this appointment has been made either by (1) directly appointing the region on the image surface with a light pen, a joy stick or a tablet or by (2) inputting numerical data concerning the coordinate values of the region to be displayed and the magnification through a keyboard.
The first appointing method (1) however, is impractical in that it requires an expensive light pen, tablet or the like. The second appointing method (2) is also defective in that it requires a highly complicated and troublesome operation for inputting the coordinate information and that the appointment of the region cannot be made promptly.
In the techniques concerned with the image display, particularly in the NC processing or machining, it is desirable to display, simply, rapidly and at low cost, only the desired portion of the image at an enlarged or reduced scale. Unfortunately, the aforementioned conventional appointing methods (1) and (2) fail to meet this requirement.
Accordingly, there is an increasing demand for an image display system which can easily and rapidly appoint the region of the image to be displayed and enlarge or reduce the scale at which the image is displayed.